Communications system

ABSTRACT

A target communications device receiving from a source communications device a notification that a user communications device is to be handed over from that source communications device, provides the source communications device with multiple component carrier information for use by the user communications device. The multiple component carrier information includes information indicating to the user communications device which of the multiple component carriers is to be used for initial access. The multiple component carrier information may be component carrier indexes. Communication devices may exchange component carrier indexes during a setup or updating procedure such as an X2 setup or updating procedure.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/983,879, filed May 18, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/482,155, filed Apr. 7, 2017, (now U.S. Pat. No.10,004,015) which is a continuation of U.S. patent application Ser. No.15/147,275, filed May 5, 2016, (now U.S. Pat. No. 9,713,052), which is acontinuation of U.S. patent application Ser. No. 13/390,485, filed Feb.14, 2012 (now U.S. Pat. No. 9,363,719), which is a National Stage Entryof International Application No. PCT/JP2010/063794, filed Aug. 10, 2010,which claims priority from United Kingdom Patent Application No.0914353.8, filed Aug. 17, 2009. The entire contents of theabove-referenced applications are expressly incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to communications devices, particularlybut not exclusively devices operating according to the 3GPP standards orequivalents or derivatives thereof. The invention has particular hut notexclusive relevance to the impacts of carrier aggregation that is to beused in LTE-Advanced (Long Term Evolution-Advanced) as currently definedin 3GPP standards documentation TR 36.814.

BACKGROUND ART

With LTE Rel 8, a transmission hand of 20 MHz was defined. InLTE-Advanced carrier aggregation will be used to support systembandwidths up to 100 MHz. This involves splitting the system bandwidthinto five 20 MHz sub-bands, each centred on a respective componentcarrier. In order to be backwards compatible with LTE Rel 8 UserEquipment (UEs), at least one of those sub-bands has to be LTE Rel 8compliant.

It has been proposed for LTE-Advanced that, during handover, the targeteNB (that is the base station of the cell to which the UE is moving),will tell the UE (via the source eNB, that is the base station of thecell in which the UE is currently located) which Component Carriers(CCs) the UE will be assigned to in the target cell. Thus, it has beenproposed that at intra-LTE handover multiple Carrier Components (CCs)will be configured in the handover command for usage after the handover.This is to avoid the need for signalling this information to the LTEafter it arrives in the target cell so that the target eNB does not haveto configure additional Component Carriers to the UE after the handover.

DISCLOSURE OF INVENTION

In one aspect, the present invention provides a communications devicethat is configured to communicate to a UE which of a plurality ofcarrier components (CCs) configured in a handover command for usageafter the handover should be used for initial access to facilitateinitial access of the UE at handover. Dedicated preamble for the UE maybe provided from the same component carrier.

In one aspect, the present invention provides a method performed by atarget communications device, the method comprising: receiving from asource communications device a notification that a user communicationsdevice is to be handed over from that source communications device; andproviding for the user communications device multiple component carrierinformation including information indicating to the user communicationsdevice which of the multiple component carriers is to be used forinitial access.

In another aspect, the present invention provides a method performed bya source communications device, the method comprising: supplying to atarget communications device a notification that a user communicationsdevice is to be handed over to that target communications device; andreceiving from the target communications device multiple componentcarrier information for the user communications device, the multiplecomponent carrier information including information indicating to theuser communications device which of the multiple component carriers isto be used for initial access.

In another aspect, the present invention provides a method performed bya user communication device, comprising: receiving from a communicationsdevice multiple component carrier information including informationindicating to the user communications device which of the multiplecomponent carriers is to be used for initial access; and initiatinginitial access using the identified component carrier.

In another aspect, the present invention provides a targetcommunications device, the target communications device comprising: areceiver to receive from a source communications device a notificationthat a user communications device is to be handed over from that sourcecommunications device; and a provider to provide for the usercommunications device multiple component carrier information includinginformation indicating to the user communications device which of themultiple component carriers is to be used for initial access.

In another aspect, the present invention provides a sourcecommunications device, the source communications device comprising: asupplier to supply to a target communications device a notification thata user communications device is to be handed over to that targetcommunications device; and a receiver to receive from the targetcommunications device multiple component carrier information for theuser communications device, the multiple component carrier informationincluding information indicating to the user communications device whichof the multiple component carriers is to be used for initial access.

In another aspect, the present invention provides a user communicationdevice, comprising: a receiver to receive from a communications devicemultiple component carrier information including information indicatingto the user communications device which of the multiple componentcarriers is to be used for initial access; and an initiator to initiateinitial access with a target communications device using the identifiedcomponent carrier.

The multiple component carrier information may be provided to the sourcecommunications device for transmittal to the user communications device.

In an embodiment, the notification is a handover command. Theinformation indicating which of the multiple component carriers is to beused for initial access by the user communications device may beprovided in a handover request acknowledge message to the sourcecommunications device for communication to the user communicationsdevice. The handover request acknowledge message may include atransparent container to be sent to the user communications device, forexample sent as a Radio Resource Control message.

In an embodiment, the multiple component carrier information indicatesthat a dedicated preamble is allocated from the component carrier to beused for initial access.

In an embodiment or embodiments, the component carrier informationcomprises a component carrier index for each carrier.

Component carrier information may be exchanged with one or inureneighbouring communications devices, for example during a setup orupdating procedure such as an X2 interface setup or updating procedure,with that neighbouring communications device.

The carrier component information may be used for signalling, forexample for signalling on the X2 and Uu interfaces.

In another aspect, the present invention provides a method performed bya target communications device, the method comprising: receiving from asource communications device a notification that a user communicationsdevice is to be handed over from that source communications device; andproviding for the user communications device multiple component carrierinformation comprising a component carrier index for each componentcarrier.

In another aspect, the present invention provides a method performed bya source communications device, the method comprising: supplying to atarget communications device a notification that a user communicationsdevice is to be handed over from that source communications device; andreceiving for the user communications device multiple component carrierinformation comprising a component carrier index for each carrier.

In another aspect, the present invention provides a method performed bya communications device, the method comprising the communications deviceusing carrier components indexes for signalling purposes while at leastone of configuring, activating and deactivating multiple carriercomponents.

In another aspect, the present invention provides a method performed bya communications device, the method comprising the communications devicesupplying multiple component carrier information to a neighbouringcommunications device and receiving multiple component carrierinformation from a neighbouring communications device during setup orupdating of a communication interface such as an X2 interface with thatneighbouring communications device.

In another aspect, the present invention provides a targetcommunications device, the target communications device comprising: areceiver to receive from a source communications device a notificationthat a user communications device is to be handed over from that sourcecommunications device; and a provider to provide for the usercommunications device multiple component carrier information comprisinga component carrier index for each carrier.

In another aspect, the present invention provides a sourcecommunications device, the source communications device comprising: asupplier to supply to a target communications device a notification thata user communications device is to be handed over from that sourcecommunications device; and a receiver to receive for the usercommunications device multiple component carrier information comprisinga component carrier index for each carrier.

In another aspect, the present invention provides a communicationsdevice comprising a supplier to supply multiple component carrierinformation to a neighbouring communications device and a receiver toreceive multiple component carrier information from a neighbouringcommunications device during setup or updating of a communicationinterface such as an X2 interface with that neighbouring communicationsdevice.

In one aspect, the present invention provides a communications devicethat provides a component carrier index which both a UE and thecommunications device can use for the signaling purposes, for examplewhile at least one of configuring, activating and deactivating multiplecarrier components.

In an embodiment, a component carrier index is used to indicate to a UEthe component carrier on which the initial access is to be performed inthe target cell after handover.

In one aspect, the present invention provides a communications devicethat exchanges component carrier information with a neighboringcommunications device, that is a communications device of a neighboringcell in a cellular network, so that a component carrier index providedto a UE is known also to the neighboring communications device.

In an embodiment, component carrier information of neighboringcommunications device is exchanged during the setup or updating of theX2 interface between the two communications devices and the carriercomponent index is known in the neighboring communications device. Thesecarrier component indexes can be used for signaling on the X2 interfaceand on the air interface between the UTRAN and the UE (the Uuinterface).

In an embodiment, a target communications device receiving from a sourcecommunications device a notification that a user communications deviceis to be handed over from that source communications device, providesthe source communications device with information for multiple componentcarriers (multiple component carrier information) for use by the usercommunications device. The multiple component carrier informationincludes information indicating to the user communications device whichof the multiple component carriers is to be used for initial access. Themultiple component carrier information may be component carrier indexes.Communication devices may exchange component carrier indexes during asetup or updating procedure such as an X2 setup or updating procedure.

The invention provides, for all methods disclosed, correspondingcomputer programs or computer program products for execution oncorresponding equipment, the equipment itself (user equipment,communication devices or nodes, or components thereof) and methods ofupdating the equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a mobile telecommunication system of atype to which the invention is applicable;

FIG. 2a schematically illustrates a generic frame structure used incommunications over the wireless links of the system shown in FIG. 1;

FIG. 2b schematically illustrates the way in which the frequencysubcarriers are divided into resource blocks and the way that a timeslot is divided into a number of OFDM symbols;

FIG. 3 schematically illustrates a base station forming part of thesystem shown in FIG. 1;

FIG. 4 schematically illustrates a mobile telephone (UE) forming part ofthe system shown in FIG. 1;

FIG. 5 is a block diagram illustrating the main components oftransceiver circuitry forming part of the mobile telephone shown in FIG.4;

FIG. 6 illustrates one example of a handover process; and

FIG. 7 illustrates an X2 set up procedure.

BEST MODE FOR CARRYING OUT THE INVENTION

Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 in which a user of a UE (User Equipment, that is a mobiletelephone (otherwise referred to as cellular telephones or cell phones)or other device capable of communicating over a mobile (cellular)telecommunication system) 3-0, 3-1, and 3-2 can communicate with a userof another UE (shown or not shown) via one of the base stations 5-1 or5-2 and a telephone network 7. The mobile (cellular) telecommunicationsystem 1 is made up of a number of cells or geographical areas, each ofwhich has a base station 5. A UE within a cell may communicate with thatcell's base station and UEs may move between neighbouring cells whichrequires a handover process to hand over communication with the UE fromthe base station of its current cell (the source base station) to thebase station of the cell to which it is moving (the target basestation).

A number of uplink mid downlink communications resources (sub-carriers,time slots etc) are available for the wireless link between the UEs 3and the base stations 5. In this embodiment, a base station 5 allocatesdownlink resources to a UE 3 depending on the amount of data to be sentto the UE 3. Similarly, a base station 5 allocates uplink resources to aUE 3 depending on the amount and type of data that the UE 3 has to sendto the base station 5.

In this embodiment, the system bandwidth is divided into five 20 MHzsub-bands, each being carried by a respective component carrier. Thebase station 5 is operable to allocated resources for each UE 3 on oneor more of the component carriers, depending on the capability of the UE3 concerned and the amount of data to be transmitted between the basestation 5 and that UE 3. The UEs 3 have transceiver circuitry that canreceive and transmit signals on the different component carriers andwhen the UE 3 is not scheduled to use a particular component carrier, itcan power down the corresponding transceiver circuitry to conservebattery power.

LTE Sub Frame Data Structure

In the access scheme and general frame structure agreed for LTE Rel 8,an Orthogonal Frequency Division Multiple Access (OFDMA) technique isused for the downlink to allow the UEs 3 to receive data over the airinterface with the base station 5. Different sub-carriers are allocatedby the base station 5 (for a predetermined amount of time) to each UE 3depending on the amount of data to be sent to the UE 3. These arereferred to as physical resource blocks (PRBs) in the LTEspecifications. PRBs thus have a time and frequency dimension. To dothis, the base station 5 dynamically allocates PRBs for each device thatit is serving and signals the allocations for each sub-frame (TTI) toeach of the scheduled UEs 3 in a control channel.

FIG. 2a illustrates a generic frame structure agreed for LTE Rel 8communications over the air interface with the base station 5. As shown,one frame 13 is 10 msec (milli-second) long and comprises ten sub-frames15 of 1 msec duration (known as a Transmission Time Interval (TTI)).Each sub-frame or TTI comprises two slots 17 of 0.5 msec duration. Eachslot 17 comprises either six or seven OFDM symbols 19, depending onwhether the normal or extended cyclic prefix (CP) is employed. The totalnumber of available sub-carriers depends on the overall transmissionbandwidth of the system. The LTE specifications define parameters forsystem bandwidths from 1.4 MHz to 20 MHz and one PRB is currentlydefined to comprise 12 consecutive subcarriers for one slot 17. A PRBover two slots is also defined by the LTE specifications as being thesmallest element of resource allocation assigned by the base stationscheduler. These sub-carriers are then modulated onto a componentcarrier to up-convert the signal to the desired transmission bandwidth.The transmitted downlink signal thus comprises N_(BW) subcarriers for aduration of N_(symb) OFDM symbols. It can be represented by a resourcegrid as illustrated in FIG. 2b . Each box in the grid represents asingle sub-carrier for one symbol period and is referred to as aresource element. As shown, each PRB 21 is formed from 12 consecutivesub-carriers and (in this case) seven symbols for each subcarrier;although in practice the same allocations are made in the second slot 17of each sub-frame 15 as well.

At the start of each sub-frame 15, the base station 5 transmits a PDCCH(Physical Downlink Control Channel) over the first three symbols. Theremaining symbols form the PDSCH (Physical Downlink Shared CHannel)which is used to carry the downlink user data for the UEs 3. The PDCCHchannel includes, among other things, data for each of the UEs 3,indicating if the UE 3 is scheduled for receiving downlink data in thatsub-frame or is scheduled for uplink transmission in that sub-frame; andif so, data identifying the PRBs to be used for receiving the downlinkdata or for transmitting the uplink data.

LTE-Advanced

In the proposed LTE-Advanced system, a number of separate sub-bands willbe provided in order to support wider transmission bandwidths, each ofthe sub-bands will at least be similar in structure to the LTE structurediscussed above. The sub-carriers for each sub-band will be modulatedonto a separate component carrier so that the transmitted sub-bands arecontiguous or non-contiguous with each other. This is known as carrieraggregation. If there are five sub-bands each 20 MHz wide, then thetotal system bandwidth will be 100 MHz. In the following description,the terms sub-band and component carrier will be used interchangeably.

Although LTE-Advanced UEs 3 will support bandwidths up to 100 MHz, theymay not transmit/receive in the whole spectrum at any given time. Inorder to allow the UEs 3 to save battery power the system is preferablyarranged so that the UEs 3 monitor one or a subset of the componentcarriers to start with; and then the base station scheduler, based onthe activity of the UE 3, can direct the UE 3 to monitor a different(although perhaps overlapping) subset of the component carriers.

Base Station

FIG. 3 is a block diagram illustrating the main components of each ofthe base stations 5 shown in FIG. 1. As shown, each base station 5includes transceiver circuitry 31 to transmit signals to and to receivesignals from the UEs 3 via one or more antennae 33 and to transmitsignals to and to receive signals from the telephone network 7 via anetwork interface 35. A controller 37 is provided to control theoperation of the transceiver circuitry 21 in accordance with softwarestored in memory 39. The software includes, among other things, anoperating system 41 and a communications control module 43 having aresource allocation module 45 and a scheduler module 47. Thecommunications control module 43 is operable to control the generationof the sub-frames in the different sub-bands in which the uplink anddownlink data is transmitted from/to the UEs 3. The resource allocationmodule 45 is operable to allocate the resource blocks in the differentsub-bands to be used by the transceiver circuitry 31 in itscommunications with each of the UEs 3, depending on the amount of datato be transmitted between the base station 5 and the UEs 3. Thescheduler module 47 is operable to schedule the times for thetransmission of the downlink data to the UEs 3 and the times for the UE3 to transmit its uplink data to the base station 5. The communicationscontrol module 43 is responsible: for signalling, to each of the UEs 3,data identifying which component carriers the UE should be monitoringwhen in the Idle mode; and for moving the UEs 3 between the differentcomponent carriers when in RRC Connected mode; and for defining the DRXpatterns used for controlling the times when the UEs 3 can switch offits transceiver circuitry.

User Equipment (UE)

FIG. 4 is a block diagram illustrating the main components of each ofthe UEs 3 shown in FIG. 1. As shown, the UEs 3 include transceivercircuitry 71 that is operable to transmit signals to and to receivesignals from the base station 5 via one or more antennae 73. As shown,the UE 3 also includes a controller 75 which controls the operation ofthe UE 3 and which is connected to the transceiver circuitry 71 and to aloudspeaker 77, a microphone 79, a display 81, and a keypad 83. Thecontroller 75 operates in accordance with software instructions storedwithin memory 85. As shown, these software instructions include, amongother things, an operating system 87 and a communications control module89 that includes a resource allocation module 91 and a transceivercontrol module 93. The communications control module 89 is operable tocontrol communications with the base station 5 and during the Idle modemonitors an anchor component carrier. The resource allocation module isresponsible for identifying the resources on which uplink should betransmitted and on which downlink data is to be received in thedifferent sub-hands. The transceiver control module 93 is responsiblefor identifying the parts of the transceiver circuitry 71 that can beswitched off at the current instance using, for example, DRXconfiguration data received from the base station 5 or using knowledgeof the sub-hands that the UE 3 is to monitor.

In the above description, the base stations 5 and the UEs 3 aredescribed for ease of understanding as having a number of discretemodules (such as the resource allocation modules, scheduler module,transceiver control module etc.). Whilst these modules may be providedin this way for certain applications, for example where an existingsystem has been modified to implement the invention, in otherapplications, these modules may be built into the overall operatingsystem or code and so these modules may not be discernible as discreteentities.

As mentioned above, LTE-Advanced UEs 3 have transceiver circuitry 71that can transmit and receive data on a number of different componentcarriers. FIG. 5 is a block diagram illustrating suitable transceivercircuitry 71 that may be used. As shown, the transceiver circuitryincludes five up-converter/down-converter circuits 95-1 to 95-5, one foreach of the five sub-bands, for modulating and demodulating thesub-carriers onto the corresponding component carrier (C1 to C5). Thetransceiver circuitry 71 also includes five encoding/decoding circuits97-1 to 97-5 for encoding and decoding the uplink data and downlink datarespectively in each of the five sub-bands. The encoding/decodingcircuits 97 receive the uplink data from, and pass the decoded downlinkdata to, the controller 75. The controller 75 also supplies individualpower control signals (via the dashed signal lines) to theencoding/decoding circuits 97 and to the up-converter circuits 95, sothat individual circuits can be powered down when not needed and so thatthey can all be powered down when none of the circuits are needed (forexample when the UE 3 enters its sleep mode).

The communications control module 43 (FIG. 3) of the target base stationis configured to indicate to the UE which of the multiple componentcarriers (five in the example above) configured for that UE is to beused by that UE for initial access and the dedicated preamble allocatedfrom that same one of the multiple component carriers, so that, afterthe handover, the target base station does not have to configureadditional component carriers to the UE and does not have to identify tothe UE which of the multiple component carriers is to be used forinitial access.

In an example, the target base station may provide the Component CarrierInformation to a UE by providing the UE with a Component Carrier Indexfor each of the multiple carrier components configured for that UE. TheUE and the base station may use these indexes to identify a carriercomponent, for example while configuring, activating and deactivatingone or more of the multiple carrier components. These indexes may bestored in a component carrier index store 48 of the communicationscontrol module 43 of the base station and a component carrier indexstore 88 of the communications control module 89 of the UE 3.

FIG. 6 illustrates the proposed intra-MME/Serving Gateway Handover (HO)procedure and shows C—Plane Handover (HO) Signalling with a singlecarrier where the communications control module 43 (FIG. 3) of thetarget base station is configured to indicate to the UE which of themultiple component carriers configured for that UE is to be used by thatUE for initial access.

The HO procedure is performed without EPC involvement, i.e. preparationmessages are directly exchanged between the eNBs. The release of theresources at the source side during the HO completion phase is triggeredby the eNB.

-   -   0 The UE context within the source eNB (eNodeB) contains        information regarding roaming restrictions which were provided        either at connection establishment or at the last TA update.    -   1 The source eNB configures the UE measurement procedures        according to the area restriction information. Measurements        provided by the source eNB may assist the function controlling        the UE's connection mobility.    -   2 UE is triggered to send MEASUREMENT REPORT by the rules set by        i.e. system information, specification etc.    -   3 Source eNB makes a decision based on MEASUREMENT REPORT and        RRM information to hand off UE.    -   4 The source eNB issues a HANDOVER REQUEST message to the target        eNB passing necessary information to prepare the HO at the        target side (UE X2 signalling context reference at source eNB,        UE S1 EPC signalling context reference, target cell ID,        K_(eNB*), RRC context including the C-RNTI of the UE in the        source eNB, AS-configuration, E-RAB context and physical layer        ID of the source cell+MAC for possible RLF recovery). UE X2/UE        S1 signalling references enable the target eNB to address the        source eNB and the EPC. The E-RAB context includes necessary RNL        and TNL addressing information, and QoS profiles of the E-RABs.    -   5 Admission Control may be performed by the target eNB dependent        on the received E-RAB QoS information to increase the likelihood        of a successful HO, if the resources can be granted by target        eNB. The target eNB configures the required resources according        to the received E-RAB QoS information and reserves a C-RNTI and        optionally a RACH preamble. The AS-configuration to be used in        the target cell can either be specified independently (i.e. an        “establishment”) or as a delta compared to the AS-configuration        used in the source cell (i.e. a “reconfiguration”).    -   6 Target eNB prepares HO with L1/L2 and sends the HANDOVER        REQUEST ACKNOWLEDGE to the source eNB. The HANDOVER REQUEST        ACKNOWLEDGE message includes a transparent container to be sent        to the UE as an RRC message to perform the handover. The        container includes a new C-RNTI, target eNB security algorithm        identifiers for the selected security algorithms, may include a        dedicated RACH preamble, and possibly some other parameters i.e.        access parameters, SIBs, etc. For LTE Advanced, this message        will carry multiple carrier configuration information and the        information on which carrier to be used for initial access and        the dedicate preamble from the same carrier. The HANDOVER        REQUEST ACKNOWLEDGE message may also include RNL/TNL information        for the forwarding tunnels, if necessary.

NOTE: As soon as the source eNB receives the HANDOVER REQUESTACKNOWLEDGE, or as soon as the transmission of the handover command isinitiated in the downlink, data forwarding may be initiated.

Steps 7 to 16 provide means to avoid data loss during HO and are furtherdetailed in 10.1.2.1.2 and 10.1.2.3 of the 3GPP Specifications 36.300EUTRAN Overall Description Stage 2.

-   -   7 The target eNB generates the RRC message to perform the        handover, i.e RRC Connection Reconfiguration message including        the mobilityControl Information, to be sent by the source eNB        towards the UE. The source eNB performs the necessary integrity        protection and ciphering of the message. The UE receives the RRC        Connection Reconfiguration message with necessary parameters        (i.e. new C-RNTI, target eNB security algorithm identifiers, and        optionally dedicated RACH preamble, target eNB SIBs, etc.) and        is commanded by the source eNB to perform the HO. The UE does        not need to delay the handover execution for delivering the        HARQ/ARQ responses to source eNB.    -   8 The source eNB sends the SN STATUS TRANSFER message to the        target eNB to convey the uplink PDCP SN receiver status and the        downlink PDCP SN transmitter status of E-RABs for which PDCP        status preservation applies (i.e. for RLC AM). The uplink PDCP        SN receiver status includes at least the PDCP SN of the first        missing UL SDU and may include a bit map of the receive status        of the out of sequence UL SDUs that the UE needs to retransmit        in the target cell, if there are any such SDUs. The downlink        PDCP SN transmitter status indicates the next PDCP SN that the        target eNB shall assign to new SDUs, not having a PDCP SN yet.        The source eNB may omit sending this message if none of the        E-RABs of the UE shall be treated with PDCP status preservation.    -   9 After receiving the RRC Connection Reconfiguration message        including the mobilityControl Information, UE performs        synchronisation to target eNB and accesses the target cell via        RACH, following a contention-free procedure if a dedicated RACH        preamble was indicated in the mobility Control Information, or        following a contention-based procedure if no dedicated preamble        was indicated. UE derives target eNB specific keys and        configures the selected security algorithms to be used in the        target cell.    -   10 The target eNB responds with UL allocation and timing        advance.    -   11 When the UE has successfully accessed the target cell, the UE        sends the RRC Connection Reconfiguration Complete message        (C-RNTI) to confirm the handover, along with an uplink Buffer        Status Report, whenever possible, to the target eNB to indicate        that the handover procedure is completed for the UE. The target        eNB verifies the C-RNTI sent in the RRC Connection        Reconfiguration Complete message. The target eNB can now begin        sending data to the UE.    -   12 The target eNB sends a PATH SWITCH message to MME to inform        that the UE has changed cell.    -   13 The MME sends an UPDATE USER PLANE REQUEST message to the        Serving Gateway.    -   14 The Serving Gateway switches the downlink data path to the        target side. The

Serving Gateway sends one or more “end marker” packets on the old pathto the source eNB and then can release any U-plane/TNL resources towardsthe source eNB.

-   -   15 Serving Gateway sends an UPDATE USER PLANE RESPONSE message        to MME.    -   16 The MME confirms the PATH SWITCH message with the PATH SWITCH        ACKNOWLEDGE message.    -   17 By sending UE CONTEXT RELEASE, the target eNB informs success        of HO to source eNB and triggers the release of resources by the        source eNB. The target eNB sends this message after the PATH        SWITCH ACKNOWLEDGE message is received from the MME.    -   18 Upon reception of the UE CONTEXT RELEASE message, the source        eNB can release radio and C-plane related resources associated        to the UE context. Any ongoing data forwarding may continue.

As set out above, for LTE Advanced, the HANDOVER REQUEST ACKNOWLEDGEmessage will carry multiple carrier component configuration informationand the information on which carrier component to be used for initialaccess and the dedicate preamble from the same carrier component. Thisinformation may use carrier component indexes as discussed above toidentify the different carrier components.

In an example, the communications control modules 43 of the basestations 5 are configured to enable Component Carrier Information, forexample the indexes mentioned above, to be exchanged between the twobase stations during a communications setup or updating procedure, inthis example an X2 setup or updating procedure, so that these carriercomponent indexes can be used be for signaling, for signaling on the X2and Uu interfaces in this example. FIG. 7 illustrates a successfuloperation.

The X2 setup procedure is described in sections 8.3.3.1 and 8.3.3.2 of36.423 of the 3GPP Specifications. FIG. 7 illustrates a successful setupprocedure.

The purpose of the X2 setup procedure is to exchange application levelconfiguration data needed for two base stations to interoperatecorrectly over the X2 interface. This procedure erases any existingapplication level configuration data in the two base stations andreplaces it by the one received. This procedure also resets the X2interface as a Reset procedure would do. The procedure uses nonUE-associated signalling.

Thus, in this setup procedure, a base station (eNB1 in FIG. 7) initiatesthe X2 setup procedure by sending an X2 SETUP REQUEST message to acandidate base station (eNB2 in FIG. 7). The candidate base station eNBreplies with the X2 SETUP RESPONSE message. The initiating base stationeNB1 transfers a list of served cells and, if available, a list ofsupported GU Group Ids to the candidate base station eNB2. The candidatebase station eNB2 replies with a list of its served cells and includes,if available, a list of supported GU Group Ids in the reply.

The initiating base station eNB1 may include Neighbour Information IE inthe X2 SETUP REQUEST message. The candidate base station eNB2 may alsoinclude the Neighbour Information IE in the X2 SETUP RESPONSE message.The Neighbour Information IE only includes E-UTRAN cells that are directneighbours of cells in the reporting eNB, where a direct neighbour ofone cell of eNB2 may be any cell belonging to an eNB that is a neighbourof that eNB2 cell e.g. even if the cell has not been reported by a UE.

In this example, Component Carrier Information is included in the X2SETUP REQUEST and X2 SETUP RESPONSE messages and so is exchanged duringthe X2 setup procedure. Generally this Component Carrier Informationwill be Component Carrier Indexes which can thus be used for signallingon the X2 and Uu interfaces.

Carrier index information can also be included in X2 ENB CONFIGURATIONUPDATE and ENB CONFIGURATION UPDATE ACKNOWLEDGE in case the new carrieris added or existing one deleted.

In an embodiment, a target communications device 5 receiving from asource communications device 5 a notification that a user communicationsdevice 3-0, 3-1, 3-2 is to be handed over from that sourcecommunications device, provides the source communications device withmultiple component carrier information for use by the usercommunications device. The multiple component carrier informationincludes information indicating to the user communications device whichof the multiple component carriers is to be used for initial access. Themultiple component carrier information may be component carrier indexes.Communication devices may exchange component carrier indexes during asetup procedure such as an X2 setup procedure, which indexes can then beused for signalling on the X2 and Uu interfaces.

Modifications and Alternatives

As those skilled in the art will appreciate, a number of modificationsand alternatives can be made to the above-described embodiments whilststill benefiting from the inventions embodied therein. By way ofillustration only a number of these alternatives and modifications willnow be described. These alternatives and modifications may be used aloneor in any combination.

The examples described above indicate that there are five carriercomponents for LTE-Advanced. It will of course be appreciated that thisis for compliance with LTE-Advanced and that the number of carriercomponents could be fewer or less. The features described above may beused alone or in combination. Thus, for example the target base stationmay indicate which, out of the configured component carriers, shall beused by the UE for the initial access by use of component carrierindexes or in another fashion. Component Carrier Information may beexchanged by the neighboring base station cells during the setup of theX2 interface between the two base station using Component CarrierIndexes or in another fashion. Component Carrier Indexes may be usedsimply for signaling purpose while configuring, activating anddeactivating multiple carrier components.

In the above embodiments, a telephone based telecommunications systemwas described. As those skilled in the art will appreciate, thesignalling and power control techniques described in the presentapplication can be employed in any communications system. In the generalcase, the base stations and the CIEs can be considered as communicationsnodes or devices which communicate with each other. Other communicationsnodes or devices may include user devices such as, for example, personaldigital assistants, laptop computers, web browsers, etc.

In the above embodiments, a number of software modules were described.As those skilled will appreciate, the software modules may be providedin compiled or un-compiled form and may be supplied to the base stationor to the UE as a signal over a computer network, or on a recordingmedium or may be directly installed or provided as firmware. Further,the functionality provided by part or all of this software may beprovided by one or more dedicated hardware circuits or any suitablecombination of two or more of software, firmware and hardware. However,the use of software modules is preferred as it facilitates the updatingof base station 5 and the UEs 3 in order to update theirfunctionalities. Similarly, although the above embodiments employedtransceiver circuitry, at least some of the functionality of thetransceiver circuitry may be provided by software or firmware or anysuitable combination of two or more of software, firmware and hardware.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

Glossary of 3GPP Terms

-   LTE—Long Term Evolution (of UTRAN)-   eNodeB—E-UTRAN Node B-   UE—User Equipment—mobile communication device-   DL—downlink—link from base to mobile-   UL—uplink—link from mobile to base-   MME—Mobility Management Entity-   UPE—User Plane Entity-   HO—Handover-   RLC—Radio Link Control-   RRC—Radio Resource Control-   RRM—Radio Resource Management-   SAE—System Architecture Evolution-   C-RNTI—Cell-Radio Network Temporary Identifier-   SIB—System Information Block-   U-plane—User Plane-   X2 Interface—Interface between two eNodeB-   S1 Interface—Interface between eNodeB and MME-   TA—Tracking Area-   EPC—Evolved Packet Core-   AS—Access Stratum-   RNL—Radio Network Layer-   TNL—Transport Network Layer-   RACH—Random Access Channel-   MU MIMO—Multi-User Multi Input Multi Output-   DMRS—Demodulation Reference Signal Format-   MCS—Modulation and Coding Scheme-   E-RAB—Evolved Radio Access Bearer-   PDCP-SN—Packet Data Convergence Protocol Sequence Number-   RLC AM—Radio Link Control Acknowledge Mode-   UL SDU—UpLink Service Data Unit-   X2 ENB—X2 eNodeB

The following is a detailed description of the way in which the presentinventions may be implemented in the currently proposed 3GPP standard.Whilst various features are described as being essential or necessary,this may only be the case for the proposed 3GPP standard, for exampledue to other requirements imposed by the standard. These statementsshould not, therefore, be construed as limiting the present invention inany way.

1. Introduction

At the RAN 2 #66 bis meeting in Los Angeles, RAN2 discussed the issue ofConnected Mode Mobility with Carrier Aggregation for LTE Advance. We hadidentified that some issues related to the measurement and haverequested RAN 4 guidance on these issues. However apart from theseissues we have also agreed that it shall be possible at intra-LTEhandover to configure multiple CCs in the “handover command” for usageafter the handover. In this contribution we focus on the handoversignaling and discuss some additional information that would be neededin order to make the initial access in the target cell.

2. Discussion

We have agreed that it shall be possible at intra-LTE handover toconfigure multiple CCs in the handover command for usage after thehandover. We see that there are benefits of this approach as the targeteNB shall not have to configure additional component carriers to the UEafter the Handover. Although one may argue that the Target eNB may firstconfigure only one component carrier for the UE. Subsequently, after thehandover, the Target eNB may then configure additional componentcarriers to the UE. But with the second approach additional signalingwould be needed in the target cell.

In the first approach where target eNB configures multiple carriercomponent during the handover it is reasonable to assume that the UEwill perform initial access in the target cell only on one componentcarriers in the cell. Moreover when we will have multiple carriercomponents which are part of a cell we need to allocate dedicatedpreamble only from one of the component carrier for the UE to performinitial access.

For LTE advance we will probably need the concept of the ComponentCarrier Index which both the UE and the eNB can use for the signalingpurpose while configuring, activating and deactivating multiple carriercomponents and also for indicating the component carrier on which theinitial access is to be performed in the target cell after handover.

Proposal 1: For LTE advance we may need the concept of the ComponentCarrier Index which both the UE and the eNB can use for the signalingpurpose while configuring, activating and deactivating multiple carriercomponents.

Proposal 2: When configuring multiple component carriers duringhandover, Target eNB also needs to indicate which, out of the configuredcomponent carrier, shall be used by the UE for the initial access andthe dedicate preamble form same component carrier shall be allocated.

Further it is reasonable to assume that the Component CarrierInformation of the neighboring eNB cells is exchanged during the setupof the X2 interface between the two eNB and the carrier component indexare known in the neighboring eNB. Although this is a RAN 3 issue, but ifwe agree in RAN 2 to use this kind of approach it would be good toliaise with RAN 3 to have consistent definition on the Uu and X2interface for the carrier component index.

Proposal 3: Component Carrier Information of the neighboring eNB cellsis exchanged during the setup of the X2 interface between the two eNBand the carrier component index is known in the neighboring eNB. Thesecarrier component indexes can be used for signaling on X2 and Uuinterface.

Carrier index information can also be included in X2 ENB CONFIGURATIONUPDATE and ENB CONFIGURATION UPDATE ACKNOWLEDGE in case the new carrieris added or existing one deleted.

3. Conclusions

In this paper we discuss what additional signaling details would beneeded while configuring multiple component carriers during connectedmode mobility and also for the details of how the UE connected mode beassigned to monitor a subset of carriers. The main proposals of thecontribution are

Proposal 1: For LTE advance we may need the concept of the ComponentCarrier Index which both the LJE and the eNB can use for the signalingpurpose while configuring, activating and deactivating multiple carriercomponents.

Proposal 2: When configuring multiple component carriers duringhandover, Target eNB also needs to indicate which, out of the configuredcomponent carrier, shall be used by the UE for the initial access andthe dedicate preamble form same component carrier shall be allocated.

Proposal 3: Component Carrier Information of the neighboring eNB cellsis exchanged during the setup of the X2 interface between the two eNBand the carrier component index is known in the neighboring eNB. Thesecarrier component indexes can be used for signaling on X2 and Uuinterface.

Carrier index information can also be included in X2 ENB CONFIGURATIONUPDATE and ENB CONFIGURATION UPDATE ACKNOWLEDGE in case the new carrieris added or existing one deleted.

While this invention has been described in terms of the embodiment, thisinvention is not limited thereto. The structure and details of thisinvention can be applied with various changes that can be understood bya person skilled in the art within the sprit and scope of this inventiondescribed in the claims.

This application is based upon and claims the benefit of priority fromUnited Kingdom Patent Application No. 0914353.8, filed on Aug. 17, 2009,the disclosure of which is incorporated herein in its entirety byreference.

The invention claimed is:
 1. A method performed by a target basestation, the method comprising: transmitting to a source base station,by a X2 SETUP REQUEST message, information related to a first componentcarrier, used for initial access with the target base station, among aplurality of component carriers that are aggregated in carrieraggregation, and information related to a second component carrier amongthe plurality of component carriers; receiving from the source basestation, a Handover Request message comprising a Cell Radio NetworkTemporary Identifier (C-RNTI) of a user equipment (UE); transmitting tothe source base station, a Handover Request Acknowledge messagecomprising first information indicating a first index related to thefirst component carrier and second information indicating a second indexrelated to the second component carrier, wherein the source base stationtransmits the first and second information to the UE; and communicatingwith the UE on the first component carrier and the second componentcarrier aggregated in Carrier Aggregation.
 2. The method of claim 1,wherein the Handover Request Acknowledge message further comprises thirdinformation indicating a dedicated preamble used for initial access withthe target base station on the first component carrier.
 3. The method ofclaim 1, wherein the Handover Request message comprises informationrelated to the first component carrier and information related to thesecond component carrier.
 4. A method performed by a source basestation, the method comprising: receiving from a target base station, bya X2 SETUP REQUEST message, information related to a first componentcarrier, used for initial access with the target base station, among aplurality of component carriers that are aggregated in carrieraggregation, and information related to a second component carrier amongthe plurality of component carriers; transmitting to the target basestation, a Handover Request message comprising a Cell Radio NetworkTemporary Identifier (C-RNTI) of a user equipment (UE); and receivingfrom the target base station, a Handover Request Acknowledge messagecomprising first information indicating a first index related to thefirst component carrier and second information indicating a second indexrelated to the second component carrier, wherein the first componentcarrier and the second component carrier aggregated in CarrierAggregation are used for communication between the target base stationand the UE.
 5. The method of claim 4, wherein the Handover RequestAcknowledge message further comprises third information indicating adedicated preamble used for initial access with the target base stationon the first component carrier.
 6. The method of claim 4, wherein theHandover Request message comprises information related to the firstcomponent carrier and information related to the second componentcarrier.
 7. A target base station comprising a transceiver configuredto: transmit to a source base station, by a X2 SETUP REQUEST message,information related to a first component carrier, used for initialaccess with the target base station, among a plurality of componentcarriers that are aggregated in carrier aggregation, and informationrelated to a second component carrier among the plurality of componentcarriers; receive from the source base station, a Handover Requestmessage comprising a Cell Radio Network Temporary Identifier (C-RNTI) ofa user equipment (UE); transmit to the source base station, a HandoverRequest Acknowledge message comprising first information indicating afirst index related to the first component carrier and secondinformation indicating a second index related to the second componentcarrier, wherein the source base station transmits the first and secondinformation to the UE; and communicate with the UE on the firstcomponent carrier and the second component carrier aggregated in CarrierAggregation.
 8. The target base station of claim 7, wherein the HandoverRequest Acknowledge message further comprises third informationindicating a dedicated preamble used for initial access with the targetbase station on the first component carrier.
 9. The method of claim 7,wherein the Handover Request message comprises information related tothe first component carrier and information related to the secondcomponent carrier.